This invention relates to conveyor ovens used to cook food. More particularly, this invention relates to conveyor ovens that cook foods using infrared energy.
Heat transfer occurs in at least one of three ways: conduction; convection and radiation. Conduction requires direct physical contact between two objects, such as when pan-flying foods. Convection relies on heat transfer via a liquid or gas. In a conventional, i.e., convection oven, heated air molecules bump into other molecules, and transfer some of their energy. Radiant heat, i.e., infrared heat, is different. It heats by the transfer of electromagnetic energy; it does not rely on any intermediary to conduct heat because it works directly on molecules in its path.
FIG. 1 depicts the relationship between IR radiation emitted from a surface as a function of wavelength at various surface temperatures. Surfaces temperatures above about 2000 degrees C. will emit relatively short wavelength IR that is in the visible spectrum. Short wavelength IR is also known to penetrate materials more deeply than long wavelength IR. At surface temperatures below 900 degrees C., the emitted IR is of a much longer wavelength, less “intense” and less penetrating.
Since all heat transfer involves some loss, radiant cooking is more energy efficient because less energy is lost heating a conductor, whether the heat conductor is a solid material or the air enclosed in a conventional oven. Cooking with infrared heat is therefore faster and more energy efficient than either conduction or convention.
Conveyor ovens that cook using infrared heat that is provided by electric resistance are slow to heat, slow to cool and slow to adjust their heat output levels, but their control is relatively straightforward. In general, gas-fired appliances, including ovens, heat quickly and cool quickly, however, infrared heat is difficult to controllably generate from gas combustion and it's output wavelength and intensity is difficult to adjust, in part because adjusting the volumetric flow rate of a fuel gas through a gas valve is difficult to do. A conveyor oven that can tale advantage of infrared energy supplied by both gas and electric energy sources would be an improvement over the prior art.